Multiple regions of 1720 MHz OH maser emissions (with \(V_{\text{LSR}}\)  ranging between 5 and 15\(\,{}\) ), loosely distributed in six areas (A–F) [1]} were also found towards the north eastern regions of W28 (see Fig.REF ). These masers were found to be preferentially located along the interface between the shock and the interacting molecular cloud, supporting the hypothesis that they were excited due to the interaction between the two [2]}, [3]}. The APEX observations discussed in the present paper were carried out towards the F group of OH masers shown in Fig. REF .
